Melitastro

I started getting the messages about incompatibility a few weeks ago, running a mini pc at the mount, laptop for control and desktop for processing. The mini and laptop are now running Linux, and since I've found proton will run most of my games (the only things i have that are Windows specific) I'll be switching to Linux on the desktop soon. The only thing that still needs Windows is the iOptron firmware program but everything else is happy with Linux (Kstars / Ekos / Pixinsight etc)

10 hours ago, Clarkey said:

I have an RC8 and have spent many hours going round in circles trying to get it 'perfect'. Eventually I came to the conclusion that with the cheaper GSO RC's this was as good as I was going to get. I would say you are about as close as you are likely to get by eye. The inner spot is indicative of good collimation (the name eludes me). The DSI collimation procedure is quite good for star tests, but I found a method using a combination of the TS RC collimator (secondary) and star testing (primary) worked well.

The only thing I am planning to do is get a ronchi grating to get the FL of the mirrors spot on. Some seem to quite along way from the published FL.

Thanks, I haven't seen mention of the TS RC Collimator before, so I'll give that a look and see what sort of results people have managed with it

3 hours ago, GalaxyGael said:

Agree that you are in the close-enough territory. I asked earlier in the thread if you use the tilt adapter for the focuser, since that is one way to deal with the offset ghost in stars. your secondary might be fine and the relationship between the primary and the focuser could have a slight nudge. But that would mean checking all three again as they have a tight relationship. Not to worry if you have done that, but if you have the tilt adapter and have not done so, you might dial it in given you are able to get it this far with the collimation.

OK, thanks, I'll probably leave well alone seeing as you agree that it's looking pretty good. I don't want to spoil anything now I've got it this close 🙂

5 hours ago, licho52 said:

With the cheap RC and I now have the 8" version, at some point I consider it to be "close enough"  I found that if I don't I tend to make it worse and then spend another few hours playing with collimation screws....while mumbling foul words incoherently.

I think you've reached the "close enough point."  Trying to be a perfectionist with these scopes is self-destructive!

Thank you, I think those are wise words. Unless someone out there can make a rigorous analysis from those images I'm going to leave it as it is 🙂

2 hours ago, newbie alert said:

This may help to show what proceedure is needed to adjust what part..

 

Thanks, I've viewed this before, but it doesn't touch on analysing star images to get an idea of what is causing the collimation error

Tony

3 hours ago, GalaxyGael said:

Do you use a tilt adapter to which your focuser is attached? 

Yes, I have one in the imaging chain

I've just finished cleaning and setting up my scope after moving to a new home. The collimation seems pretty close but obviously needs a final tweak and I'm not sure exactly what adjustments are needed to get it spot on

This is the focused image:

This is defocused inwards, with the lower image showing some detail of the bright star:

And finally, defocused outwards:

Does anyone have some advice on the steps to follow to complete the collimation? I don't want to adjust the wrong mirror, or adjust them in the wrong order and find I'm making things worse!

Tony

I'm the owner of a GSO RC6 and have just come across this discussion. One point that stands out is that the consensus of opinion for adjusting the secondary mirror to achieve the optimal focal length is by adjusting the centre screw on the secondary support. I'm not convinced this is the best way as the mirror distance can be adjusted by slacking the locking ring (see photo) and screwing the housing in or out as needed.

It's much easier than using the centre screw and in theory will not mess up the collimation.  However @davies07's post says that Es Reid used the centre screw adjustment method so I'd really like clarification on this as I must be missing something.  A better view of the secondary mirror housing construction can be found on Han Kleijn's site http://www.hnsky.org/RC_collimation.htm

Tony

8 hours ago, apophisOAS said:

I suppose it wasn't anything to do with Focus ,  sorry to ask but how did you focus with the Baader as opposed to the Astrodon it was a different focus point ?

Stars are naff in the best NB images apparently anyway.

Regards

Roger

I can't remeber 100% which star, there are plenty available from my site. It would have been a 2nd or 3rd mag using APT with Bahtinov aid and mask. Recorded the focus point for each (I'm using a Pegasus focus cube) and then used the same difference between focus positions when imaging.

Tony

53 minutes ago, Petergoodhew said:

I had halos with Baader OIII filters too.  I then discovered that they had made a faulty batch of OIII filters and this was the reason for the halos.  Eventually Baader agreed to replace my filter free of charge on condition that I returned the faulty filter. My new Baader OIII filter has no halos.

Mine will have come from stock held by Teleskop Service in 2015, I wonder if they are from the same batch?

8 minutes ago, Whirlwind said:

It comes down to what halos are and what causes them.  Baader are correct in this statement to some extent, although the commentary on professional telescopes also having halos isn't really relevant (professional telescope filters are set for maximising throughput not pictures).  

Halos are in effect defocussed images of the star.   To get a halo off a filter you need it to reflect light from a source.  This could be, for example light reflecting off the cover slip back on to the filter that then gets re-reflected back towards the CCD.  The light path for this is much longer than the focal length and hence by the time the light gets to the CCD it is way out of focus (hence the halo).  Alternatively the light may reflect off the filter onto a reducer/flattener glass and then be reflected back towards the CCD.  The same effect is seen.  A cover slip that transmits almost 100% of the light and has a very effective anti reflective coating hence shouldn't have halo issues with *any* filter as nothing is being reflected back on to the filter.  On the other hand a filter with extremely effective anti-reflective coating would not reflect light as well and prevent the halos (e.g. astrodon).  If both have anti reflection issues then you will get halos.  

As such it is not impossible that the some combinations work and some don't with any filter.  I'm not sure of the set up here but it is some form of reflector so if there is a flattener/reducer/coma corrector in the way you could try removing this and seeing if you still have the halos.  If they are still there then the chances the reflection is between the CCD cover slip and the filter.  If it goes away then you may find that a flattener/reducer/coma corrector with excellent AR properties (or possibly longer back focus to spread the light so far that it is not visible) may solve the problem.  

If it is between the cover slip and the filter then you probably will need new filters or a camera with better anti-reflective characteristics (which might be cheaper given the price of astrodons!)

As I mention, there are no other optics in the path, these are taken with just the filter and no reducers or flatteners etc. and the camera is ASI 1600MM-Pro at -10°C that has what ZWO refer to as the 'protective window' over the sensor

14 minutes ago, continuum said:

I also have the same experience and have been pondering on other makes of OIII filters. Because Astrodon prices are stratospheric I have been considering Astronomik or Optolong.  Does anyone have experience of these brands?

Ron

I'm starting to realise how widespread this issue is. Has anyone had good experience with this filter?

5 minutes ago, Xplode said:

Looking at the small halo it's easy to tell it's a reflection from within a filter.
Did you try to reverse the filter?
It can for certain help because you will switch side of the reflective side of the filter.

No I didn't, as I say in my post I didn't try to screw it in from the other side. Is that really a solution that's used with mounted filters, I've only seen it discussed with unmounted ones?

Back in 2016 I bought the Baader LRGBC + Narrowband 1.25" filter set. For various reasons I only used the LRGB and didn't use the narrow band filters until a few weeks ago.  Those of you who've bought these filters will know they advertise 'NO halos, NO reflections, NO ghosting' on the filter case, so I was really surprised when the images through the OIII filter had a really well defined halo.

I looked on Baader's website and contact with them is by using a web form so I posted a description of my filters, a copy of my NB images (Ha, SII and OIII) and a list of the equipment in my imaging train, and asked for their feedback on the OIII image.  However, their reply was a copy and paste - or "Because we have such inquiries regulary, we wrote a complete, detailed explanation about such effects" - which more or less said that the problem was most likely due to other optics in the imaging chain (there were none, only their filters) or the window in front of the camera or spacing of the optical elements (none again).  The problem is everything but their filter.  It even suggested reversing the filter, something I've never seen suggested before for a mounted filter.  Are you supposed to dismantle the FW so you can insert it from the back of the carousel? They even had the cheek to try and sell me on the aesthetic value of having halos because they even occur around bright stars when imaging nebulae (ok, we've all seen Alnitak in the Horeshead nebula photos!).  They concluded with "Most likely you cannot get rid of the Halo - unless using extensive image processing such as described by our customer Andreas Bringmann in the attached pdf".

Having been in charge of management systems before I retired, my approach to problem solving is a bit different to theirs, and with so few variables to consider the use of a different OIII filter seemed obvious.  Although I can't really afford it, I opted for the Astrodon 5nm as it is supposed to be the standard by which others are judged. The filter arrived yesterday and these are last night's results comparing the Baader and Astrodon - identical 100s exposures for each, the only difference being the refocus between images.

I think the images speak for themselves, so when customer service tell you:

what they actually mean is "Most likely you cannot get rid of the Halo - unless..." you stop using our filters!!

PS: I've got a Baader OIII filter going cheap - I'm saving for some more Astrodon NB filters 🙂

Tony

The only thing I can think of, and you've probably done it when cleaning the sensor, is making sure the holes in the carousel are clear so the sensor can detect position correctly.

Tony

How's this? If you need a different view then let me know

Would an image of 7 x 1.25" help?